I'm gonna have to go with this. Reluctantly.

must've. it's a word now because I said so. That red line is irrelevant because I'm better than autocorrect because I said so. god has spoken.

You know, "must've" is a word too.

EDIT: damn it WD

Except, when you're saying it, it's more like "must o'", so there's no point in pretending you're actually saying "must've".

Bollocks! You can't justify bad grammar just because "it sounds better". You stupid kids! Grrrrr! You can say "must of" phonetically but if you're writing it then it is "must have". Did you ever see a newspaper (remember them kids?) where the columnist said "The man must of been guilty?" Me arse! Stop trying to wriggle out of it and admit you have been caught by Das Naszischen Grammenbanfurhrer! Expect us when you least expect us.

Also "must've" is a shortened version, I'm sure you know, of "must have" --- "of" does not have "v" or "e" in it...

Again, stupid kids! Buy a dictionary! NO not online! Gaaaahhhhh!
http://d2ws0xxnnorfdo.cloudfront.net/meme/260500

**** that ****. Do I read like I'm trying to pretty up the way I walk in real life? I only professor my **** up when I'm debatin'.

It's official, you're a hillbilly.

I hope you choke on your clam chowdah.

You're writing pal, not speaking. Stop making excuses. Do it right, or you'll be drummed out of the Grammar Nazis.

Again, **** that ****. I spell real good, and I gots perdy punctuation. Good 'nuff for me. And until you start capitalizing song and album titles, then you have no room to talk.